In both humans and rats dopaminergic drugs in small doses facilitate male sexual behavior. In a program designed to locate the sites in the brain at which these drugs act, we have shown that the dopamine (DA) agonist, apomorphine (APO), infused into the medial preoptic area (MPOA), the nucleus accumbens (NA), and the lateral ventricles (LV), affected male sexual behavior in dose related and, at least partially, regionally specific ways. The MPOA is known to be especially important for the regulation of masculine sexual behavior, and our infusions into the MPOA produced more dramatic results than infusions into other areas. One goal of the proposed research is to investigate further the relative importance of the MPOA and of several other DA containing areas (spinal cord, ventral tegmental area, and lateral septal area) in dopaminergic regulation of masculine sexual behavior. A second goal is to specify the receptor mechanisms that mediate the effects of APO infusions. The importance of DA receptors, as opposed to other receptors or nonspecific membrane effects, will be inferred if APO's effects are blocked by a DA receptor antagonist and if infusions of the antagonist produce results opposite to those of APO. In addition, the roles of D-2 receptors and of autoreceptors will be assessed by infusing a specific D-2 agonist and an autoreceptor agonist into the MPOA. A pattern of results similar to APO's, produced by either of these agonists, will suggest that APO acted on the respective receptor. The third goal is to clarify hormone-transmitter interactions and their significance for sexual behavior. The effects of several hormonal manipulations on DA biochemistry and on behavior will be studied. In addition, correlation coefficients will be computed between the resultant biochemical and behavioral changes. Finally, DA biochemistry of inherently good and poor copulators will be compared. Systemically administered DA drugs can facilitate masculine sexual behavior; however, systemically administered drugs affect numerous systems simultaneously. A better understanding of the specific biochemical mechanisms within critical brain areas that regulate masculine function should improve treatment of sexual dysfunction.